DRAM (Dynamic Random Access Memory) widely used in a storage apparatus as a cache memory is volatile and may be subjected to a data loss as a result of possible power outage or the like.
Thus, to prevent a possible data loss, many storage apparatuses back up data by transferring data stored in the cache memory to a nonvolatile memory medium when the power goes down. To ensure that the data stored in the cache memory is reliably backed up, battery capacity needs to be increased to allow a backup process to be normally carried out until the process is completed.
However, the increased battery capacity increases the costs of the storage apparatus. Thus, as a technique for supporting the backup process with a small battery capacity, a technique is used which involves saving of unwritten data on the cache memory (PTL 1). According to this conventional technique, the data in the cache memory is temporarily saved to a save area in a particular disk apparatus at the time or power outage or the like. Thus, large-capacity data is saved to the disk apparatus in a short time.